Human papilloma virus is a small double-stranded DNA virus that colonizes various stratified epithelia like skin, oral and genital mucosa, and induces the formation of self-limiting benign tumors known as papillomas (warts) or condylomas. Most of these benign tumors naturally regress due to the influence of host immunological defenses. Some HPVs, however, have oncogenic potential and have been associated with certain types of cancers. See, Lorincz et al., Obstetrics & Gynecology, 79:328-337 (1992); Beaudenon et al., Nature, 321:246-249 (1986); and Holloway et al., Gynecol. Onc., 41:123-128 (1991).
HPV is the most prevalent, sexually transmitted virus. More than 35 HPV genotypes are known to be sexually transmitted, but a relatively few genotypes account for the majority of ano-genital infections. Among these most common HPV types are two forms with high risk for carcinogenic progression (HPV16 and HPV18), and two forms that cause the majority of genital warts (HPV6 and HPV11).
An estimated 5.5 million people become infected with HPV each year in the United States, and an estimated 20 million Americans are currently infected (Cates and et al., Lancet, 354, Suppl. SIV62, 1999). Approximately 75 percent of the male and female reproductive-age population has been infected with sexually transmitted HPV, though the main public health risk is to women through cervical cancer (Koutsky, Am. J. Med., 102(5A), 3-8, 1997). Thus, millions of people in the U.S. alone require treatment each year. It's important to note that PAP smears represent the largest public health screening program in the world, and that the test is, essentially, a measure of HPV infection. The current standard for managing a positive PAP smear is “follow up”. In general, no treatment is recommended unless an advanced stage of cervical dysplasia is observed (CDC Sexually Transmitted Diseases Treatment Guidelines, 2002).
Significant need exists in HPV positive patients for effective HPV antiviral drugs. At present no specific treatments exist for HPV or warts. Aldara™ (Imiquimod), a non-specific immunomodulator used for treating external genital warts, is the most successful treatment on the market. An effective, specific HPV treatment has the potential to significantly improve upon, and effectively compete with, Imiquimod.
The majority of human cervical carcinomas (95%) contain and express HPV DNA and it is the expression of two viral oncoproteins, E6 and E7, that appears to be critical for cellular transformation and maintenance of the transformed state. Specifically, four HPV types (HPV16, HPV-18, HPV-31, and HPV-45) have been connected to 75-93% of the cases of cervical cancer in the United States. It has been estimated that perhaps twenty percent (20%) of all cancer deaths in women worldwide are from cancers that are associated with HPV.
Generally speaking, HPVs are grouped into types based on the uniqueness of their DNA sequence.
HPVs can be further classified as either high- or low-risk on the basis of the clinical lesions with which they are associated and the relative propensity for these lesions to progress to cancer. Low risk types, such as HPV types HPV-1, HPV-2, HPV-3, HPV-4, HPV-5, HPV-7, HPV-8, and HPV-9 cause common warts (verrucae vulgaris), plantar warts (verrucae plantaris), mosaic warts, flat warts (verrucae plane), and butcher warts. Furthermore, HPV types HPV-6 and HPV-11 cause warts of the external genitalia, anus and cervix. High-risk types, such as HPV-16, HPV-18, HPV-31, HPV-33 and HPV-45 are particularly common in intraepithelial carcinomas, neoplasias and cancers. In particular, the genomes of two HPV types, HPV-16 and HPV-18, have been found to be associated with about 70% of invasive carcinomas of the uterine cervix.
Current treatment for HPV infection is extremely limited. Management normally involves physical destruction of the wart by surgical, cryosurgical, chemical, or laser removal of infected tissue. Some of these current treatments, like laser removal and surgery, are expensive and require the use of anesthesia to numb the area to be treated. Cryosurgical removal requires the use of special equipment. Furthermore, most patients experience moderate pain during and after the procedure.
Topical creams and solutions such as preparations of 5-fluorouracil, imiquimod, cidofovir, formaldehyde, glutaral, cimetidine, trichloroacetic acid, bleomycin, podofilox and podophyllum preparations have also been used. (Reichman in Harrison's 7 Principles of Internal Medicine, 13th Ed. (Isselbacher et al., eds.); McGraw-Hill, Inc., NY (1993) pp. 801-803). Recurrence after these treatments, however, is common, most likely due to the fact that the virus remains latent within the skin cells. Therefore, subsequent repetitive treatments must be used, which can destroy healthy tissue. These treatments are not available or approved for treatment of cervical infections.
Interferon has so far been the most effective treatment for HPV; however, its effectiveness is limited. (Chang et al. (2002) Journal of Virology 76: 8864-74, found some cells infected with HPV genomes became resistant to interferon treatment after only a few applications). See also Cowsert (1994) Intervirol. 37:226-230; Bornstein et al. (1993) Obstetrics Gynecol. Sur. 4504:252-260; Browder et al. (1992) Ann. Pharmacother. 26:42-45.
There is a need for therapeutics for treating a number of diseases and conditions as outlined in this application.